1. Field of the Invention
This invention relates to a bar-shaped light guide for converting light from a point light source into beam light, a beam lighting device using the bar-shaped light guide, and a surface lighting device using the beam lighting device.
2. Description of Prior Art
A beam lighting device, as shown in FIG. 16, for converting light emitted from a point light source such as a light emitting diode (LED) into beam light by a light guide is known. This beam lighting device includes point light sources 250, 250 on both end surfaces 211, 211 of a bar-shaped light guide 210, and a plurality of V-shaped grooves 225 are formed along a longitudinal direction of the bar-shaped light guide 210 on a reflecting surface 216 opposite to a light emitting surface 213. The light emitting surface 213 is a side surface of the light guide 210 in a longitudinal direction. The bar-shaped light guide 210 is a right prism comprising the light emitting surface 213, the reflecting surface 216, and side surfaces 212, 215 orthogonal to the light emitting surface 204 and the reflecting surface 216. With this structure, a part of light beam 290G incident from the point light source 250 into the bar-shaped light guide 210 reaches at an inclining surface 226 of the V-shaped groove 225 formed on the reflecting surface 216 and is reflected on the inclining surface 226. The reflected light reaches at the light emitting surface 213 at an angle smaller than a critical angle of the light emitting surface 213 and is emitted from the light emitting surface 213. The rest of the light beam incident into the bar-shaped light guide 210 reflects repeatedly within the light-emitting surface 213 and the reflecting surface 216 until the light reaches at the light emitting surface 213 at an angle smaller than the critical angle. On this principle, light emitted from the light emitting surface 213 can be distributed approximately evenly by adjusting a pitch and depths of the V-shaped grooves 225, resulting in achieving a beam light source.
As a beam light source of a lighting device for a liquid crystal display, JP 2000-11723, A discloses a surface lighting device, which uses a light source comprising a point light source and a bar-shaped light guide.
A light source described in this publication is a point light source arranged in a periphery of an end part of a light guide having light path converting means. The light path converting means includes grooves having a triangle shape in cross section, and a flat part formed between the grooves. The publication describes one example of the light path converting means, which a pitch between the grooves are uniform and a depth of the groove gradually increases as a distance from the point light source to the groove increases, and further describes another example of the light path converting means, which the depth of the grooves is uniform and a pitch between the grooves decreases as the distance from the point light source to the flat part increases.
The surface lighting device described in the publication uses two point light sources, arranged on both end parts of the bar-shaped light guide, and the point light sources are respectively arranged on a side end surface of a transparent substrate and face to the light guide.
In conjunction with this, the above structure, particularly as shown in FIG. 16, the bar-shaped light guide 210 has a rectangular shape in cross section with a uniform thickness. Therefore, the reflecting surface 216 is parallel to an optical axis of the light from the point light source 250, and lot of the light incident from the incident surface 211 does not irradiate the reflecting surface 216. As a result, light 290H which is perpendicular to the light incident surface 211 and is incident to a point higher than the depth of the V-shaped groove 225 can not reach at the reflecting surface 216, resulting in reduced light utilization efficiency of the incident light.
On the other hand, light, which enters the incident surface 211 in slant, reflects repeatedly between the light emitting surface 213, the reflecting surface 216, and both of the side surfaces. Then, the light reaches at the inclining surface 226 on the light source side of the V-shaped groove 225 formed on the reflecting surface 216, is reflected on the inclining surface 226, reaches at the light emitting surface 213, and is emitted from the light-emitting surface 213 with an angle smaller than a critical angle of the light-emitting surface 213.
FIG. 17 illustrates a surface lighting device using the beam lighting device shown in FIG. 16. The light emitting surface 213 of the light guide 210 of the beam light source is positioned in a periphery of a side end surface of the light guide plate 280. The light guide 210 is held on a side end surface of the light guide plate 280 by a reflector 270 having a reflection function.
As shown in FIGS. 16 and 17, however, when the height P of the light emitting surface 213 in cross-section of the bar-shaped light guide 210 is longer than the width Q of side surfaces 212 and 215, an area occupied by the V-shaped grooves 225 of the bar-shaped light guide 210 in cross section is reduced. Therefore, the light, which repeats reflection between the light-emitting surface 213, the reflecting surface 216, and the side surfaces 212 and 215, does not reach at the inclining surface 226 on the light source side of the V-shaped groove 225 formed on the reflecting surface 216 (see FIG. 16), and the ratio of light reaching at the inclining surface 226 to all the light becomes low. Thus, the number of light beams which do not reach to the reflecting surface 216 but pass through the surface opposite to the light incident surface 211 increases, resulting in further reduction of utilization efficiency of the incident light.
An incident angle of light which is directly incident to the inclining surface 226 on the light source side of the V-shaped groove 225 in the periphery of the incident surface 211 at which the light intensity is high, and an incident angle of light which is incident to the inclining surface 226 of the V-shaped groove 225 far from the light incident surface 211 are different. Therefore, as shown in FIG. 18, viewing angle characteristics of light emitted from the light emitting surface 213 varies depending on places. FIG. 18 illustrates angle distribution of light emitted from the bar-shaped light guide 210 at three points; in a periphery of the light incident surface 211 on a left side, at the center, and in a periphery of the light incident surface 211 on a right side. Needless to say, the angle distribution of the emitted light can be observed at any places.
To use such the beam light source as a light source for a light guide plate, for example, a diffusing sheet 261 and a lens sheet 262 should be arranged on the side of the light-emitting surface 213 for correcting light, resulting in degraded productivity caused by an increase in cost and the number of assemble processes.
This invention was made to improve utilization efficiency of an incident light.
Also it is an objective of the present invention to uniform viewing angle characteristics of light emitted from a light emitting surface at any spots of a bar-shaped light guide and to reduce costs and the number of assembly processes so as to improve the productivity.
A bar-shaped light guide of this invention comprises a light incident surface for receiving light emitted from a point light source, a light emitting surface, which is orthogonal to the light incident surface, for emitting the light received on the light incident surface in a form of beam light, a pattern surface made up of a side of the light incident surface and a side of the light emitting surface and including a plurality of grooves formed thereon. The plurality of the grooves are regularly arranged on the pattern surface, and an angle formed by the groove and the side of the light emitting source is 35-55xc2x0 on a side of the point light source.
With this structure, main component of light emitted from the point light source is reflected on the grooves and the light is emitted from the light emitting surface in an approximately vertical line direction. Therefore, utilization efficiency of incident light can be improved. Furthermore, viewing angle characteristics of the light emitted from the light emitting surface can be uniform at any spots of the bar-shaped light guide.
A bar-shaped light guide of this invention comprises a first light incident surface for receiving light emitted from a first point light source, a second light incident surface, which is opposite to the first light incident surface, for receiving light emitted from a second point light source, a light emitting surface, which is orthogonal to a plurality of the light incident surfaces, for emitting light received on the plurality of the light incident surfaces in a form of beam light. The bar-shaped light guide further includes a first pattern surface made up of upper sides of the plurality of the light incident surfaces and an upper side of the light emitting surface and including a plurality of grooves regularly formed, where an angle formed by the upper side of the light emitting surface and the groove is 35-55xc2x0 on a side of the first point light source, and a second pattern surface opposite to the first pattern surface and including a plurality of grooves regularly formed, where an angle formed by a bottom side of the light emitting surface and the groove is 35-55xc2x0 on a side of the second point light source.
With this structure, light of high intensity can be emitted from the light emitting surface.
A bar-shaped light guide of this invention comprises a light incident surface for receiving light emitted from a point light source, and a light emitting surface, which is orthogonal to the light incident surface, for emitting light received on the light incident surface in a form of beam light. The bar-shaped light guide further includes a first pattern surface made up of an upper side of the light incident surface and an upper side of the light emitting surface and including a plurality of grooves regularly formed thereon, where an angle formed by the upper side of the light emitting surface and the groove is 35-55xc2x0 on a side of the point light source, and a second pattern surface, which is opposite to the first pattern surface, including a plurality of grooves regularly formed thereon, where an angle formed by the bottom side of the light emitting surface and the groove is 35-55xc2x0 on a side of the point light source.
With this structure, utilization efficiency of incident light can be further improved.
In any of the above described bar-shaped light guide, the plurality of the grooves formed on the pattern surface are formed with such a pitch that the grooves adjacent each other are partially overlapped at least in a longitudinal direction.
With this structure, utilization efficiency of incident light can be further improved.
Any of the above described bar-shaped light guide further comprises a surface opposite to the light emitting surface including a plurality of grooves regularly formed thereon.
With this structure, utilization efficiency of incident light can be completely improved
A beam lighting device of this invention comprises any of the above describe bar-shaped light guide and a point light source arranged in a periphery of the light incident surface of the bar-shaped light guide.
The beam lighting device of this structure no longer needs a diffusion sheet and a lens sheet. Consequently cost and the number of assembly process can be reduced and productivity of the beam lighting device can be improved.
A surface lighting device of this invention includes a surface light guide plate arranged on the light emitting surface of the beam lighting device. The surface light guide plate includes a light incident surface for receiving light emitted from a light emitting surface of the beam lighting device, a reflecting surface, which crosses to the light incident surface at 80-100xc2x0, for reflecting light received on the light incident surface, and a light emitting surface, which is opposite to the reflecting surface, for emitting light reflected on the reflecting surface in a form of surface light.
The surface lighting device of this structure can improve productivity of the surface lighting device.